Correct answer is Option (d) Artificial selection. Because, it does not occurs naturally. It is man made for to lead his life easily.
Artificial selection is the process of selecting desired (more wanted) trait, when breed (to cross) with other plants/animals to get desired (more wanted) traits.
Examples:- Obtaining of Dogs from Wolves, Obtaining of Kohlrabi Cauliflower, Broccoli, Cabbage, Red cabbage, Kale from Wild cabbage.
Option a, b, and c occurs naturally by leaving the option d as it is a man made process.
Hence, Option d is correct friend...